Diesel engine lubrication



May 12, 1942.

E R; BARNARD 15mm. ENGINE nupmcnron Filed Nov. '17 1937 VINVENTCIJRV Edward A. Barnard ATTORNEY Patented May 12, 1942,

DIESEL ENGINE LUBRICATION] v Edward R. Barnard, Chicago, Ill., assignor to ,2";

Standard Oil Company,

ration of Indiana Application hlovemberl'l, 1937, Serial No. 175,156

' (c1.1s4: c)

5 Claims.

This invention relates to the lubrication of internal combustion engines and more particularly internal combustion engines of the compression ignition type commonly known as Diesel engines. One object of the invention is to provide a 'method of lubricating. Diesel engines by employing a lubricant which will satisfy the requirements for lubricating the'piston and other moving parts of the engine and at the 1 same time will produce little or'no carbon deposits on the piston and piston rings which-are exposed to high temperature. Another object of the invention is to provide a lubricant of higher viscosity than previously used which will more perfectly seal the piston in the cylinder of the engine, thus reducing the extent of blow by? and enabling the engine to operate more efliciently, especially at low speeds and under low load conditions. invention is to permit operating compressionignition engines with higher compression ratios, higher loads and corresponding higher piston temperatures without serious deposition of coke in the piston rings and on the piston which would otherwise jam the piston rings and cause the pistons to seize and score the, cylinder walls, Still another object of the invention is to, provide a method of lubricatingfDiesel en.- gines of the high speed type operating at 700 to 2400 R. P. M. Other objects of the invention willbe observed from the following description.

The principal characteristic of compressionignition engines which differentiates them from' other internal combustion engines is the use of high compression suflicient to heat the air in the cylinder adiabatically toja temperature above the ignition point of the fuel. In order to accomplish this itis necessary in these engines to em.-

' ploy compression rations of to 1 and higher,

even as high as to 1', although in ordinary practice compression ratios of between 12 to 1 and 14 to 1 are used. With compression ratios of this magnitude the compression pressure developed is commonly about 500 pounds per square inch, although pressures of 375 to 400 pounds per squareinch may be employed in engines of large size. Pressures of 800-900 pounds per square inch have been employed experimentally,

but cannot be used in practice because of mechanical difliculties and particularly because of lubrication failure hereinafter more fully described. p

When employing such high cylinder pressures it is impracticable to introduce the entire fuel charge at one time because the combustion pres- Chicago, 111., acorpow sure developed would exceed the strength foifthe engine parts and also p'roduc'e severe dtonation. 'I'hereforein Diesel engine's'the fuelisjinjected gradually, extending overa considerable portion of the power stroke with. a View to 'jmaintaining a relatively const'ant pressure duringcombustlon.

As a result of the combustion bein extended over a considerable period; the absorption of heat by the pis'tonis muclrjgreater thaninordi nary internal combustion engines and serious difliculty has been encountered 'in maintaining a proper lubricationof the pistonand piston'rings.

Piston temperatures behind the touring have been :measured as high as 500-F.', atemperature sufficiently high "to"pro'duce "coking of ordinary lubricatin'g oils. The problemis even m'ore severe in thef'case-of two cycle engines than' with four cycle engines'because of the'wshorterftime Still another object'of thev of t the piston. j

' venting 'carbonization allowed between combustion fperiods tor coolin Numerous methods have been tried forj preof Diesel engine pistonsby decomposition of the" lubricating oil. It is common practice; for examplato place the top ring or compression ring anappreciable' distancejfrom v .the top of the piston. Another device. is to employ exception'ally longpistons, for example a piston length for one and 'a' half timesfthe Idi'ameter, in order to provide greater area of contact with the cooled cylinder walls,.thusassistingfin dissipating the heat. Still another method is to 7 provide a deep groove in the pis tona bove"the top compressionring so that flow of heat. from piston crown to rings is're'tar'ded by the thinner section of metal. Such groovesare calledfheat grooves or heat traps. The piston crown'thus runs at'very high temperatures to which'the oil great resistance'to carbon formation. A larger number'of rings is GustomariIyfemis exposed'onthe underside; making necessary ployed on Diesel pistons thas is used in o'rdi-' nary internal combustion engines in order to "provide better contact with the cylinder'wall'i'or conduction of heat; also to provide'f'substitute .rings to maintain compression in, case ithel top "compression ring becomes jammed with carbon and thereby rendered "inoperativei'j In "Diesel practice, for example, it: is common practice, to

employ five or six rings on the pis ton, whereas in ordinary gas enginepractice three rings usually are suflicient. "Devices for cooling Diesel pistons are commonly employed andare quite ess'entialin the larger engines havingl pistons of ten "inches in diameter orm'ore', in whichcase oil streams may be directed against the piston the piston, employing telescoping pipe connections for the purpose. Such devices, however, are impractical in the smaller high speed type engines which are the principal subject of this commanded a premium'for the lubrication of other internal combustion engines. The choice of naphthenic oils has been based largely on the fact that they produce less carbon around the piston rings. Various theories have been advanced to account for this, the most plausible explanationbeing that the naphthenicoilshave a higher vapor pressure for .a given viscosity and therefore distil away from .hot surfaces sufficiently rapidly to prevent seriouscarboniz ation. ,Volatility considerations have also prompted the use'of relatively light oils in comparison with' the oils used for other internal combustion engines. Thus in the lubrication of Diesel engines of the high speed type oils of and S. A. E.

grade are commonly used rather than the heavier oils of and 50 S. A. E. grades whose volatility is considerably less.

Now it is well understood that for thelubricationof engine parts operating at'high temperatures such as Diesel engine pistonsthe most d8.-

sirable oil would ordinarily be an oil suffering the least change in viscosity with increasein temperature and therefore, measured: by this criterion, the naphthenicor, coastal oils having very ,low viscosity 'indices,for example 0.-.to 20.

Dean and Davis, would ordinarily be avoided.

However, the higher volatility of these naphthenlcoils is such an important factor in Diesel engine operation that ,their use is commonly ,re-

quired in spite of their low viscosity index.

' Attempts to employjoils of. higher viscosity index for high speed Diesel lubrication have generally failed because of thelow volatility which characterizes such oils, resulting in deposition of hard carbon on. the piston rings -and in the ring grooves, thus requiring frequent shutting down of the engine for cleaning and overhauling.

' Inasmuch as Diesel enginesflnd their most important use in installations requiring continuous operation, such as in electric power plants, long distance trucking and bus service, tractor and marine duty, etc., it is especially inconvenient and costly to shut them down for overhauling and therefore every effort has been made by Diesel engine manufacturers and operators to avoid doing so.

' The accompanying drawing whichformsa part of this specification shows across sectional view of a typical four-strokeqcycle engine cylinder and piston with exhaust, inlet valve and fuel injector. The piston I0 is usually constructed of slightly smaller diameter at the top to allow for thermal expansion. The'piston is also reduced in diameterabove the top ring in order to provide more space for carbon deposition, thus somewhat lengthening the periods between necessary dismantling and cleaning. Therings ll located in the ring grooves I! must be carefully fitted to prevent loss of air during compresr or water may be circulated through passages in sion which is particularly serious in compressionignition engines. The cylinder wall I3 is cooled by water cooling jacket H.

After the combustion of the fuel, during the power stroke, exhaust valve [5 is opened to discharge the burning gases, following which inlet valve l6 opens to admit air, the exhaust valve having closed. The cylinder is filled with air, the inlet valve closes and the upward movement of the piston then compresses the air in the compression space I! to a pressure of about 500 pounds per square inch. The compression is sufficient to heat the air to a temperature above the ignition point of the fuel, for example about 700 F. Just as the piston approaches top dead center, ,the'fuel is injected through the fuel nozzle" 18. The fuel for a high speed type Diesel engine-is usually a distillate having approximately the characteristics of kerosene or gas oil. .Various types of fuel injectors may be employed but a-type which is most commonly used in high speed Diesel operation is the so called solid injection type in which the fuel is forced under high pressure, about 1500 pounds per square inch,

to'the nozzle l8 where it sprayed into the heated air, burning instantly during the injections The combustion of the fuel raises and sustains the pressurein the combustion space I! during the power stroke of the piston, after which the burned gases are exhausted again and the cycle repeated.

Part of the heat of the burninggases is'transmittedto the cylinder head and cylinder walls where it is removed by suitable water jacketlng as indicated. The heat which is absorbed by the piston head, however,'must necessarily be dissipated by conduction downward through the body of the piston and outward into the cylinder walls where the piston comes in contact therewith. The upper or compression'rings of the piston therefore operate at a much higher temperature 'thanthe lower rings and accordingly are the "ones which are the first to become carbonized by decomposition of the lubricating oilwhich reaches them from the cylinder walls below the piston.' Lubrlcating'oil is usually applied to the piston by forcing itthrough the crank shaft (not shown) and out through the connecting rod crank bearing I! or it may be conducted'through connecting rod c-20 and allowed to flow through suitable channels from the wrist pin bearing 2!. Excess oil applied to thecylinder walls in this way when the piston is in the upper position is wiped from the cylinder walls by oil ring 22 which leaves a uniform film of oilon the cylinder walls for lubrication of the upper part'of the piston and the upper rings. The 'oil which reaches the compression rings in this manner therefore serves not only to provide an oil film on the cylinder walls to prevent metal, contact v between the piston rings and the cylinderwalls 1 which would rapidly result in'scoring the cylinder, but also serves to seal the piston 'ringsin the grooves 12, thus assisting in maintaining the 65,

desired compression in the cylinder.

A careful study has beenmadeiof the carbonization of. lubricating oils ,in' internal combustion enginesand some of this work has been published in S. A. E. Journal, .vol. 29, 1931 (p.

215) by W. H. Bahlke, 'etal This work which was conducted. with various oils, both natural and synthetic, showed that the carbon forming tendency of the oil was substantially ininverse proportion to the volatility. Accordingly a volatility test has been devised and has provedtobe further be noted a synthetic oil made action of boron fluoride at ordinary temperatures, for example temperatures .of about F.

of thevapor when 90% has to 100 F. The resulting polymerization product is carefully distilled to remove from it theexcessively light and heavy. polymerization products which are satisfactory;

I have-found in this manner possesses far less tendency to form carbon than would be indicated by the car- Synthetic Pamflin Synthetic thene oil from m from base 9 base oil wax iggg Flash point.. 0 F. 470 395 420. 375 GravityA. P. I.. 28.1 p 21.6 30.8 32.2 Viscosity seconds at at 210 F 69. 6 56. 2 68. 2 67; 3 Viscosity index 103 24 97 91 Carbonization index. 800 467 600 550 Carbon, actual iormaggn (in 100 1r.)engine t per pis on grams '3. 7 .l. 5 '0. 5 Nil Hours required to stick rings 50-75 800 tl,000 Vt2,000

Does not include deposits on underside inside piston skirt.

TEstimated.

It will be observed that the above four typical oils all have the same viscosity at 210 F. except the naphthene base oil which has about the. same viscosity as the paraflin base oil at'-100 F. It also be noted from the above results that with the exception of the isobutylene Diesel'oil, the carbonization index bears a close relation l of piston 'crown and to the carbon actually formed in the test engine, whereas the isobutylene Diesel oil produced much would be expected. It should less carbon than that the viscosity index of the isobutylene Diesel oil is nearly as high as that of the Pennsylvania. oil,1 whereas the Pennsylvania oil produced a great. deal more carbon in the engine test. The time required to'stick rings depends largely on the amount of carbon formed.

As previously indicated, my isobutylene Diesel oil 'is made by polymerizing liquid isobutylene with boron fluoride. In carrying out this part of the process, liquid isobutylene is maintained under pressure and cooled to a temperature, for example, of about 0 C., and about 0.1% to 2% of BF: is added with vigorousagitation. Excessive rise in temperature due to the heat of reaction may be avoided by efllclent cooling. In order to facilitate agitation in handling and to assist in controlling the reaction I prefer to employ a. diluent such as hexane, liquid butane, propane, naphtha, etc., using a solution containing about of isobutylene. I may also employ the butane-butylene fraction recovered from petroleum gases, especially those gases produced a -in the cracking of facture of gasoline. This light fraction may contain about 10% to of isobutylene, the remainder being" principally butanes' and normal butylen'e. j I i It is preferred to subject the'isobutylene to the "action' of the BF: catalyst for: about minutes and thereafter recover the heavy oily product by neutralization of the excess catalyst and removal of unreacted light hydrocarbons by evaporation.

The resulting product is a viscous oil, atypical sample'of which has the following characteristics: f v Viscosity at 100 F. seconds .1"53 8 I Viscosity at 210? F -1 do 117 Viscosity index, about .101

7 Flash F 250 Pour point; do This oil, although satisfactory for many-lubrica- I Y tion problems, was found to be quite unsatisfac- .Viscosity at 100 F seconds 600 Viscosityat210 F d 0 67.3' Viscosity index 91.0 Flash vp i 1t ;;i F 375 Pour point do ..35

A. P. I. gravity 32.0 Carbonization index, about #550 above test, a

The results tory for the lubrication of Diesel engines." A"25 hour test conducted with the oil-was terminated because of an increase in viscosity of the oil of about sevenfold. No appreciable oxidation or sludging was observed in the test although the crankcase temperature was'about 300 F- It is believed thatthe large increase in viscosity was due partlyto evaporation and partly to was found ac teristics was obtained:

Thermal decomposition b'cgan' at 85% oifand533 F.

This oil was tested in a single cylinder, tractor sumption; about} pints infl60 'Oil samples for inspection purposes were taken each'30 hrs.

of this test were unprecedented, espeon the engine piston and rings.

tion, it is desirable to-fractionate the synthetic isobutylene about temperature polymerand select a fraction having to distilled at 500 F. column at 1 mm. pressure, with a carbonizapetroleum oils for the manurespect to the small amount of carbon ample 500-575? F.

Saybolt viscosity be about 550 seconds to 850 seccompounds of oxygen.

from .01% to 0.2%

tionindex of between 450 F. and 625 F), for ex- It is also desirable that the onds at 100 F. and about 55 seconds to .'7.5seconds at 210 F. Somewhat higher viscositiesthan this may be employed but if the viscosity is. too high a loss of power results from lubricating oil friction. However, the extremely low carbon-forming tendency of the isobutylene Diesel oil makes it possible to employ oils having viscosities as high as 1400 Saybolt at 100 F., corresponding to about 100 Saybolt at 210 F. In general, I prefer to employ oils having a viscosity within the range of f S. A. E. 30-40, although for some types of service I may use isobutylene polymer fractions of narlight as S. A. E. 20 and asrow boiling range as heavy as S. A. E. 50. r

In the case of operation I have observed a phenomenon known as feathering" of the piston rings and-I have discovered that this may be prevented by incorporating inthe oil small proportions of certain sulfur, phosphorus or chlo- I may add to the Diesel oil of organic sulfur compounds disulfides, lead oleate, ethyl rine. For example,

such as oil soluble l chlor stearate or calcium phenyl stearate, aluminumnaphthenate or organic 'phosphites such as tributyl and triamyl phosphite, etc. I have found that free sulfur is especially effective in concentrations between .002% and 0.2%. -I prefer to dissolve the sulfur in a portion of the oil by heating to an elevated temperature and add the desired amount of the resulting solution to the remainder of the Diesel oil. I may also dissolve the sulfur in other mineral oils or fats and add the resulting solution to the isobutylene Diesel Dieselengine under sever' operating conditions showed a pronounced feathering of the piston rings in twenty-four hours operation where the straight isobutylene Diesel oil ,was used, whereas under the same conditions, using the same oil containing .01% of sulfur, after forty-eight hours operation substantially no feathering of the piston rings was observable. To prevent this undesirable feathering efiect I prefer to employ sulfur in the amount of .01% to 0.1%, at which concentration the sulfur imparts substantially no undesirable corrosive properties to the oil.

Having thus described my invention, what I claim is:

'1. The method of preventing the feathering of piston rings in high speed Diesel engines op--' erating under high load conditions at compression pressures of 500 to 800 pounds per square inch while said piston rings are coated with a film of synthetic hydrocarbon lubricating oil having a viscosity in the range of 20 S.A. E. to 50 phorus and S A. E. motor oils" r noducedby the catalytic polymerization of liquid isobutylene at a temperature between0" F. and 100 F.,comprising dissolving in said lubricating oil 001% to 0.2% of a substance selected from the class consisting of the oil soluble compounds of oxygen, sulfurypho'schlorine. 2. The method of preventing the feathering of piston rings in high speed Diesel engines operating under high load conditions at compression pressures of 500' to 800 pounds per square inch while said piston rings are coated with a film of synthetic hydrocarbon lubricating oil having a viscosity in the range of S. A. E; to 50 S. A. E. motor oils produced by. the catalytic polymerization of liquid isobutylene at a'temcertain types of severe engine perature between 0 F. and 100 F., comprising dissolving in said lubricating oil-from .001% to 0.1% of sulfur. I

3. The method of preventing the feathering" of piston rings in high speed Diesel engines operating under high load conditions at compression pressures of at least about 375 pounds per lubricating oil. Comparative tests made on a between about 0 square inch, while said piston rings are coated with a film of a lubricant comprising predominantly a synthetic hydrocarbon oil'resulting from the polymerization of liquid isobutylene by the catalytic action of boron fluoride at a temperature between about 0 F. and F., comprising dissolving in said lubricant from about .001% to about 0.2% of a substance selected from the class consisting of oil-soluble'compounds of oxygen,

sulfur, phosphorus and chlorine.

4. The method of preventing the feathering of piston rings in high speed Diesel engines operating under high load conditions at compression pressures of at'least about 375 pounds per square inch, while said piston rings are coated with a film of a lubricant comprising predominantly a synthetic hydrocarbon oil resulting from the polymerization of liquid isobutylene by the catalytic action of boron fluoride at a temperature and100 F.,'comprising dissolving in said lubricant about 0.001% to about 0.2% of an organic phosphite.

5. The method of preventing the feathering speed Diesel engines. operating under high load conditions at compression pressures of at least about 3'75 pounds *per square inch, while said piston rings are coated lubricant comprising predominantly a synthetic hydrocarbon oil resulting from the polymerization of liquid isobutylene by the catalytic action of boron fluoride at a" temperature between about 0 F. and 100 F., comprising dissolving in said lubricant about 0.001% to about 0.2% of a chlorine-containing organic compound.

j EDWARD a. BARNARD. 

